1. Technical Field
The present invention relates to ink compositions, particularly, to an ink composition that allows formation of a recorded image with high color reproduction and light fastness.
2. Related Art
Recently, ink-jet recording with a plurality of color ink compositions has been employed to form a color image for production of a recorded material. Typically, a color image is formed using three ink compositions, namely, a yellow ink composition, a magenta ink composition, and a cyan ink composition, or four ink compositions further including a black ink composition as desired. In some cases, a color image is formed using six ink compositions including a light cyan ink composition and a light magenta ink composition in addition to the above four ink compositions, or seven ink compositions further including a dark yellow ink composition. Such combinations of two or more ink compositions are called ink sets.
Ink compositions used for forming a color image are required, for example, to have good color vividness on their own, to show a good intermediate color when combined, and to produce a recorded material that does not discolor or fade during storage.
In addition, recently, color ink-jet printers for “photo-quality” printing have been continuously improved in terms of printheads, ink compositions, recording systems, and media, and the quality thereof is comparable to “film photography.” On the other hand, the storage stability of recorded images has been improved with improvements in ink compositions and media. The light fastness, particularly, has been improved to a practically acceptable level (see JP-A-2000-290559 and JP-A-2001-288392), although it is still not comparable to that of film photography. The light fastness performance is generally evaluated on the basis of the fading rates of pure yellow (Y), magenta (M), and cyan (C) patterns (with optical densities around 1.0). If this method is used to evaluate ink compositions charged into printers currently available on the market for light fastness performance, the magenta ink composition often has the lowest performance and determines the light fastness longevity of the entire ink set. Accordingly, improving the light fastness of the magenta ink composition is effective for improving the light fastness of a photographic image and prolonging the light fastness longevity of the ink set.
In addition, printed materials produced using such ink compositions may be placed not only indoors, but also outdoors, and may therefore be exposed not only to indoor light, but also to sunlight. Accordingly, there is a need for ink compositions having high light fastness.
As colorants with high light fastness, for example, compounds (azo dyes) disclosed in JP-A-2002-371079 and compounds (anthrapyridone dyes) disclosed in JP-A-2002-332419 have been proposed. In addition, a magenta ink composition with high light fastness containing two types of colorants in combination has been proposed (see JP-A-2005-105136). To the knowledge of the inventors, however, there has so far been no known ink composition that allows formation of a recorded image with both high light fastness and high color reproduction.